Earlier this year, a separate study described a Pennsylvania patient with a rare infection that also could not be killed by Colistin, the antibiotic used by doctors when all other drugs fail to clear up an infection.

However, this current bacterial strain was collected from the New York patient during a hospital stay in 2015. Given the timetable, this is the earliest known case of this kind in the United States.

What scientists found

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For the current study, scientists at JMI Laboratories tested more than 21,000 strains of bacteria gathered from hospitals around the world. They discovered 390, nearly 2%, were resistant to Colistin. Of these, just 19 tested positive for the gene mcr-1, including the one in New York. This gene is what enables bacteria to stand up against the drug Colistin.

Despite the fact that Colistin did not kill this particular E.coli strain, other antibiotic drugs were able to destroy the infection. This may seem hopeful, but scientists are not deceived. They are concerned because the mcr-1 gene is on a piece of DNA that can move from bacteria to bacteria.

"The fear is that it will transfer to bacteria that are already resistant to most other antibiotics," explained Patrick McGann, chief of molecular research and diagnostics at Walter Reed Army Institute of Research. McGann was not involved in the study but was the lead researcher for the identification of the bacteria in the Pennsylvania patient.

The end result would be bacteria with a combined resistance to all antibiotic drugs available today --- the ultimate superbug.

While the JMI Laboratories team examined "a ton" of isolates, they found only a few with the mcr-1 gene, so the Colistin-resistant organisms are still at a "very low frequency," according to Dr. James Kirby, an associate professor of pathology at Harvard Medical School.

"I don't think something suddenly changed," he said, explaining these multi-drug resistant organisms have been around for some time now in Europe and other parts of the world but "it doesn't look like mcr-1 is suddenly taking off.

"But we now have a warning and society should stay ahead of this."

And if we do nothing?

Superbugs cause an estimated 700,000 deaths every year. If no action is taken, scientists say these numbers could rise dramatically, causing more deaths than cancer by 2050. A lack of effective antibiotics would mean common procedures such as treating wounds, giving birth and undergoing surgery could become fatal.

"Drug-resistant pathogens are notorious globe-trotters," Dr. Margaret Chan, director-general of the World Health Organization, said in a speech. Chan explained how global trade in food, global transportation and medical tourism contribute to the international spread of hospital-acquired infections that may be resistant to multiple drugs.

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Regarding the discovery of a second American patient with a Colistin-resistant infection, Kirby is prudent.

"I view this as not something we should be scared about, but it's a warning that we really need to invest in new antibiotics," he said. It's time we think carefully about how we interact with our environment, the drugs we use in animals and the drugs we use in humans, he said. We should develop a multi-pronged approach to deal with antibiotic resistance "ahead of when it becomes a disaster."